DuctWise HVAC Duct Calculator

You already know how to size a duct. This agrees with your wheel, and then answers the part the wheel cannot. Type the airflow and the friction rate. DuctWise gives you a round size the supply house actually stocks, the velocity that size will really run at, and the static the whole run will cost you — off the ASHRAE friction chart for galvanised round duct, the same chart the ductulator in your door pocket is printed from. THE PART A WHEEL CANNOT DO The round size was never the hard part. What fits in a 2x10 joist bay is. Tap once and you get every stocked rectangular size that carries the same air, squarest first, with anything past 4:1 flagged before you order it — and the flat-oval sizes beside them, for the spaces where a rectangle will not go. It is equal friction, not equal area. A 20x8 does not carry what its area suggests, because the air drags past more metal on the way…